Cushion structure

ABSTRACT

A cushioning structure effective to alleviate a blood stream trouble and loads on muscles and to prevent an outbreak of trouble caused by them such as economy-class syndrome and the like is provided. The structure includes an upper elastic member  11  composed of a three-dimensional net member formed by connecting a pair of ground knitted fabrics disposed apart from each other using connecting yarn, and a spring constant in the range of initial load during a pressurizing process is set in the range of 0.1 to 20 N/mm and, at the same time, during a restoring process, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 2 mm, is set to be lower than the spring constant in the range of initial load during the aforementioned pressurizing process. As a result, when a person comes into contact with a cushioning member by a sitting movement or a standing movement, temporal set in fatigue (stroke) of about several millimeters to about ten and several millimeters is created, thereby improving a feeling of fitting (compatibility) which makes a person feel comfortable, and effectively alleviate a blood stream trouble and loads on muscles.

TECHNICAL FIELD

[0001] The present invention relates to a cushioning structure includinga three-dimensional net member, and especially to a cushioning structuresuitable for manufacturing a seat structure and the like which reducesblood stream trouble or loads on muscles.

BACKGROUND ART

[0002] In recent years, a cushioning structure using a thin net member(three-dimensional net member) which is of a three-dimensional solidstructure, can display high cushioning property, has a large number ofpores, and is excellent in breathability has been known. Such athree-dimensional net member is built up its three-dimensional structureby connecting a pair of ground knitted fabrics disposed apart from eachother with a plenty of connecting yarns, and excellent in breathability,body pressure dispersing property, and rebounding property.

[0003] In general, when the load bearing characteristic of a cushioningmember is higher than the load bearing characteristic of the muscle, anda difference in shape between the cushioning member and the muscle islarge, the muscle is much deformed by a reaction force from thecushioning member (mainly a force in the normal line direction in a caseof rather hard cushioning member, and mainly a force in a sheardirection in case of a cushion harder than the muscle but totally thehardness being on a soft side), thereby causing the muscle to bedeformed largely, and pressed, which results in bias flow of blood orincrease of loads on muscles. On the contrary, when the load bearingcharacteristic of a cushioning member is remarkably low compared withthe load bearing characteristic of the muscle, the deformation of themuscle is restrained. However, though the amount of deformation of thecushioning member is large, since the amount of depression of thecushioning member is also large, mainly shear stress serves in play,which rather increases the loads on muscles. For instance, when softpolyurethane slab foam and viscoelastic polyurethane foam are used inpiles, though considerably soft load bearing characteristic can beobtained, compared with the case of using other materials, since theamount of deformation as a cushioning member is large, it has a problemof increase of loads on muscles due to shear stress, as described above.

[0004] In recent years, especially in an aircraft, outbreak instances ofa trouble so-called economy-class syndrome have been reported. A bloodstream trouble caused by taking the same posture for a long time insitting on a chair having a structure of supporting the femoral regionstrongly to prevent backside slipping is thought to contribute to thissyndrome. The aircraft industry are looking forward to a proposal of aseat structure which can reduce the outbreak of such an economy-classsyndrome.

[0005] The present invention is achieved in view of the above-describedpoints, and the object thereof is to provide a cushioning structureeffective to reduce blood stream trouble, loads on muscles, and toprevent the outbreak of the economy-class syndrome and the likeincluding the outbreak of troubles owing thereto.

DISCLOSURE OF THE INVENTION

[0006] As a result of assiduous studies to solve the above-describedproblems, the present inventor paid attention that when the load bearingcharacteristic of a cushioning member (elastic member) which comes incontact with the muscles directly or indirectly is made close to theload bearing characteristic of people's muscle, the cushioning memberdeforms according to the shape of the muscle, which helps to restrainlarge deformation of the muscle without setting the load bearingcharacteristic of the cushioning member softer than necessary, and iseffective to prevent blood stream trouble and the like. The presentinventor also paid attention that deformation of muscles at a portionprotruded by the bone is also reduced in the deformation, which iseffective to prevent the blood stream trouble locally. The presentinventor also paid attention that amount of the deformation can bereduced, as mentioned above, by using a three-dimensional net memberwhich can display high cushioning property even if it is thin as acushioning member (elastic member), and increase of loads on muscles dueto a shear stress created by a large deformation when a soft cushioningmember is used, and in an area of small displacement, a reaction forceinputted from the cushioning member into the muscle can be made small bysetting the load bearing characteristic to a further softer load bearingcharacteristic than that during the pressurizing process.

[0007] From these aforementioned points of view, the present inventorthought that not only a three-dimensional net member is used as acushioning member (elastic member), but also by utilizing the hysteresisloss of its load bearing characteristic, the characteristic is madeclose to the load bearing characteristic of a person in the pressurizingprocess (go-process), and made to be a softer load bearingcharacteristic with a small reaction force after the amount ofdisplacement reaches a predetermined point during the restoring process(return process), thereby movement of the body can be induced. Thepresent inventor has accomplished the present invention by thinking thatthrough this setting of the load bearing characteristic, when thecushioning member is touched at the time of a sitting movement or astanding movement, temporal set in fatigue (stroke) under loads in therange of about several millimeters to about ten and several millimetersis generated, and when a portion of a small area protruded by the boneamong the haunches portion and the like which come into contact with thecushioning member contacts with the cushioning member, the cushioningmember fits quickly with little sensing of the reaction force owing tothis temporal set in fatigue under loads so that a feeling of fitting(compatibility) which makes a person comfortable can be improved,thereby, the blood stream trouble and the loads on muscles can beeffectively reduced.

[0008] At the same time, the present inventor has also paid attentionthat when the amount of stroke is made small, and the load bearingcharacteristic in a small load area and a small displacement area untilarriving at an equilibrium point of the load is set to be soft to makethe above-described temporal set in fatigue (stroke) under loads in therange of several millimeters to ten and several millimeters, though itis effective to prevent blood stream trouble as described above, when aload more than predetermined is applied and the contact angle isincreased, this temporal set in fatigue under loads is felt to be bottomtouch. Accordingly, in the present invention, in order to prevent such afeeling of bottom touch, another elastic member which is high inlinearity and high in a feeling of a spring is arranged in two tiers orin multi-tiers in series, or is arranged to be combined in parallel.

[0009] That is, the present invention described in claim 1 is to providea cushioning structure including an elastic member composed of athree-dimensional net member formed by connecting a pair of groundknitted fabrics disposed apart from each other using connecting yarn,wherein, as a load bearing characteristic of the cushioning structure, aspring constant during a pressurizing process is set in the range of 0.1to 10 N/mm and, at the same time, during a restoring process, a springconstant after restoring to an amount of displacement of 20 mm or less,at the latest, to 2 mm, is set to be lower than the spring constant inthe aforementioned pressurizing process.

[0010] The present invention described in claim 2 is to provide thecushioning structure according to claim 1, wherein the spring constantin the aforementioned pressurizing process is set in the range of 0.1 to5 N/mm.

[0011] The present invention described in claim 3 is to provide thecushioning structure according to claims 1 or 2, wherein the amount ofhysteresis loss between the pressurizing process and the restoringprocess in the load bearing characteristic is in the range of 40 N orless.

[0012] The present invention described in claim 4 is to provide thecushioning structure according to any one of claim 1 to claim 3, whereinthe elastic member composed of the three-dimensional net member isconfigured to have a small reaction force such that as a load bearingcharacteristic during the pressurizing process the three-dimensional netmember with a board for press of 30 mm in diameter alone, a springconstant after restoring to an amount of displacement of 20 mm or less,at the latest, to 1 mm during the restoring process is lower than thespring constant during the pressurizing process in the aforementionedwhole load bearing characteristic.

[0013] The present invention described in claim 5 is to provide thecushioning structure according to claim 4, wherein the aforementionedthree-dimensional net member formed in a structure having a smallreaction force has a thickness in the range of 5 to 30 mm.

[0014] The present invention described in claim 6 is to provide thecushioning structure according to claim 4 or claim 5, wherein theaforementioned three-dimensional net member formed in a structure havinga small reaction force is provided with concave and convex portions atleast on one surface, and the elasticity of the concave portion and thatof the convex portion are different from each other.

[0015] The present invention described in claim 7 is to provide thecushioning structure according to claim 6, wherein the aforementionedthree-dimensional net member formed in a structure having a smallreaction force has a structure in which the aforementioned convexportion is formed substantially in an arch shaped cross section betweenadjacent concave portions, and the elasticity in a bending direction ofthe convex portion having the substantially arch shaped cross sectionand the damping caused by friction accompanying sliding of theconnecting yarn disposed in the concave portions can be utilized.

[0016] The present invention described in claim 8 is to provide thecushioning structure according to any one of claim 4 to claim 7, whereinanother elastic member serving as a function to prevent the cushion frombottom touch during the pressurizing process is provided below anelastic member composed of the three-dimensional net member formed in astructure with a small reaction force.

[0017] The present invention described in claim 9 is to provide thecushioning structure according to claim 8, wherein the aforementionedanother elastic member serving as a function to prevent the cushion frombottom touch is a net type elastic member, a sheet type elastic member,or a net or sheet type elastic member supported via metal springs.

[0018] The present invention described in claim 10 is to provide thecushioning structure according to claim 8 or claim 9, wherein theaforementioned another elastic member serving as a function to preventbottom touch is disposed at a predetermined interval to the elasticmember composed of a three-dimensional net member formed in a structurewith a small reaction force.

[0019] The present invention described in claim 11 is to provide thecushioning structure according to any one of claim 4 to claim 9, whereinstill another elastic member higher in surface stiffness than theelastic member composed of the three-dimensional net member formed in astructure with a small reaction force is layered, in addition to theelastic member composed of the three-dimensional net member formed in astructure with a small reaction force and aforementioned another elasticmember serving to prevent bottom touch.

[0020] The present invention described in claim 12 is to provide thecushioning structure according to claim 11, wherein an elastic membercomposed of the three-dimensional net member formed in a structure witha small reaction force is laminated on the upper portion of stillanother elastic member described above, and another elastic memberdescribed above serving as a function to prevent bottom touch isarranged on the lower portion of still another elastic member describedabove at a predetermined interval.

[0021] The present invention described in claim 13 is to provide thecushioning structure according to any one of claim 1 to claim 12,wherein the cushioning structure is applied to various seat structuresincluding a vehicle seat and a furniture chair or a mat for furniture orfor seating.

[0022] The present invention described in claim 14 is to provide thecushioning structure according to claim 13, wherein the cushioningstructure is applied to a seat structure for an aircraft.

BRIEF DESCRIPTION OF DRAWINGS

[0023]FIG. 1 is a view schematically showing the structure of acushioning structure relating to a first embodiment of the presentinvention;

[0024]FIG. 2 is a view schematically showing the structure of acushioning structure relating to a second embodiment of the presentinvention;

[0025]FIG. 3 is a view schematically showing the structure of acushioning structure relating to a third embodiment of the presentinvention;

[0026]FIG. 4 is a view schematically showing the structure of acushioning structure relating to a fourth embodiment of the presentinvention;

[0027]FIG. 5 is a view schematically showing the structure of acushioning structure relating to a fifth embodiment of the presentinvention;

[0028]FIG. 6 is a cross sectional view showing the structure of anexample of a three-dimensional net member usable in the above-describedrespective embodiments;

[0029]FIG. 7 is a view showing an example of one grand knitted fabric;

[0030]FIG. 8 is a view showing an example of the other grand knittedfabric;

[0031]FIG. 9A to FIG. 9E are explanatory views showing the way ofvarious arrangement of connecting yarn;

[0032]FIG. 10 is a perspective view showing a three-dimensional netmember provided with a concave and convex portion usable as an upperelastic member in the above-described respective embodiments;

[0033]FIG. 11 is a cross sectional view of the three-dimensional netmember shown in FIG. 10;

[0034]FIG. 12 is a view for explaining a function of substantiallyarch-shaped spring elements formed in the three-dimensional net membershown in FIG. 10;

[0035]FIG. 13 is a view for explaining the function of substantiallyarch-shaped spring elements formed in the three-dimensional net membershown in FIG. 10;

[0036]FIG. 14 is a perspective view of another three-dimensional netmember with no concave and convex portion usable as an upper elasticmember in the above-described respective embodiments, which is used intest example 1;

[0037]FIG. 15 is a graph showing a relation of load to displacementcharacteristic of three-dimensional net members alone in experiments 1to 4.

[0038]FIG. 16 is a graph showing a relation of load to displacementcharacteristic of cushioning structures relating to respectiveembodiments;

[0039]FIG. 17 is a graph showing a relation of load to displacementcharacteristic of the three-dimensional net member having the concaveand convex portion when pressurized with a board for press of 30 mm indiameter;

[0040]FIG. 18 is a graph showing a relation of load to displacementcharacteristic of the three-dimensional net member having the concaveand convex portion when pressurized with a board for press of 98 mm indiameter;

[0041]FIG. 19 is a graph showing a relation of load to displacementcharacteristic of the three-dimensional net member having the concaveand convex portion when pressurized with a board for press of 200 mm indiameter;

[0042]FIG. 20 is a view for explaining a function of a seat cushionportion applied with the cushioning structure of the present invention;

[0043]FIG. 21 is a view for explaining a function of a seat cushionportion applied with the cushioning structure of the present invention;

[0044]FIG. 22A and FIG. 22B are views for explaining a function of aseat back portion applied with the cushioning structure of the presentinvention;

[0045]FIG. 23 is a view for explaining a function of the seat backportion applied with the cushioning structure of the present invention;

[0046]FIG. 24A and FIG. 24B are views for explaining characteristics ofa seat applied with the cushioning structure of the present invention;

[0047]FIG. 25 is a graph showing a relation of load to displacementcharacteristic of the seat cushion portion applied with the cushioningstructure of the present invention;

[0048]FIG. 26 is a graph showing a relation of load to displacementcharacteristic of the seat back portion applied with the cushioningstructure of the present invention; and

[0049]FIG. 27 is a graph showing a vibration characteristic of a seatapplied with the cushioning structure of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0050] Hereinafter, the present invention will be explained in furtherdetail based on embodiments shown in the drawings. FIG. 1 is a viewshowing a cushioning structure 10 relating to a first embodiment. Thecushioning structure 10 relating to the first embodiment is formed bydisposing two elastic members 11 and 12 vertically. Between them, anupper elastic member 11 is composed of a three-dimensional net memberwith a concave and convex portion formed therein. For instance, when itis employed as a seat cushion of a seat structure, it is spread over andstrained between confronting side frames (not shown) constituting theseat structure with a predetermined elongation percentage. It should benoted that in order to ensure that the characteristics belonging to thethree-dimensional net member itself are displayed sufficiently, and tomake its load bearing characteristic close to the load bearingcharacteristic of the muscle in a small load area during thepressurizing process and to make its reaction force small in a smalldisplacement area during the restoring process by elastic deformation inthe vertical direction and in the horizontal direction at the time ofstraining, it is not recommended that it be strained with a high tensionbut with an elongation percentage of 5% or less.

[0051] An lower elastic member 12 is formed of a net type elastic membersuch as Plumaflex or a sheet type elastic member. When the cushioningstructure 10 is employed, for instance, in a seat structure as describedabove, it is supported by engaging with one end of a metal spring 15through the metal spring 15 engaging at the other end thereof with sideframes (not shown) which strains the upper elastic member 11 or with aframe member and the like disposed at a lower portion of the side frame.It is preferable that the spring characteristic created by the lowerelastic member 12 and the metal spring 15 be high in linearity than thatof the upper elastic member 11 composed of a three-dimensional netmember, and a spring constant of 35 N to 100 N by a board for press of98 mm in diameter when combined with the upper elastic member 11 isclose to the spring constant of the muscle of the haunches. On the otherhand, though the upper elastic member 11 is high in surface stiffnessagainst pressure over a large area at a force of 20 N or less, thepartial spring constant measured by pressing the concave portion and inthe vicinity of the convex portions on both sides of the concave portionwith a board for press of about 30 mm in diameter to about 20 mm indiameter is set to be smaller than the spring constant created by thelower elastic member 12 and the metal spring 15 because of its shapebeing provided with a ridge composed of concave and convex portions.Through this configuration, it creates temporal set in fatigue underloads as described above, when a protruding portion of the body comesinto contact with the seat, it becomes easy to settle partially (referto FIG. 13), and a feeling of fitting is improved.

[0052] As will be described later, the upper elastic member 11 composedof a three-dimensional net member has a thickness of about 5 mm to about30 mm, the amount of displacement stroke in the vertical direction issmall, and the load bearing characteristic in a small displacement areais extremely small and has little reaction force. Accordingly, when anapplied load meets or exceeds a predetermined value, a person sitting onthe cushion may feel the bottom touch. Therefore, a restoring force ofthe upper elastic member 11 is made up by the lower elastic member 12having a spring characteristic high in linearity and the metal spring 15so that the feeling of bottom touch is prevented by the elastic force ina load area where the predetermined load is exceeded.

[0053] It should be noted that it is possible to structure in a mannerthat the spring characteristic created by the above described lowerelastic member 12 and the metal spring 15 is possessed by the lowerelastic member alone composed of a net type elastic member or sheet typeelastic member having surface stiffness. In other words, it is possibleto use the lower elastic member alone which has a spring characteristicincluding the spring characteristic of the metal spring together withhigh surface stiffness. Needless to say, in this case, the lower elasticmember is directly strained over the side frames.

[0054] Though the upper elastic member 11 and the lower elastic member12 can be disposed to come into contact with each other when no load isapplied, it is preferable to dispose them a little apart from each otherwhen the cushion structure is employed in the seat cushion of a seatstructure for instance. Through this arrangement, since the upperelastic member 11 itself has a predetermined amount of stroke till ittouches the lower elastic member 12, a feeling of fitting in a smallload area and a small displacement area due to deformation in thevertical direction and elongation in the horizontal direction of theupper elastic member 11 can be further improved.

[0055]FIG. 2 is a view showing one example of a cushioning structure 20relating to a second embodiment of the present invention. In the secondembodiment, the cushioning structure is formed of three layers composedof an upper elastic member 21, a lower elastic member 22 and a middleelastic member 23 disposed in the middle of both the upper and lowerelastic members. The upper elastic member 21 is composed of athree-dimensional net member having concave and convex portions, and hasa same function as the upper elastic member 11 relating to theabove-described first embodiment. The lower elastic member 22 iscomposed of a net type elastic member such as Plumaflex or the likewhich is formed by putting, metal wires together for instance, or asheet type elastic member such as a three-dimensional net member or thelike, disposed to an appropriate frame members or the like forming, forinstance, a seat structure via a metal spring 25, so that the similarfunction to the lower elastic member 12 relating to the above-describedfirst embodiment is provided.

[0056] The middle elastic member 23 is composed of a three-dimensionalnet member, and disposed to be layered under the upper elastic member 21between side frames of the seat cushion which forms a seat structure,for instance. The middle elastic member 23 is higher in surfacestiffness than the upper elastic member 21 which is provided to displaya soft load bearing characteristic as described above in a small loadarea, when the load area becomes a predetermined area or more, and isprovided to prevent depression more than necessary, to increase afeeling of stability at the time of being seated or lying owing to afeeling of the stiffness, and at the same time, to restrain a feeling ofbottom touch of the upper elastic member 21 similarly to the lowerelastic member 22. Moreover, it is provided to reduce a feeling ofsomething foreign caused by the metal spring 25 or the side frames. Itshould be noted that a reaction force against a seated person can bedrastically reduced by disposing either the upper elastic member 21 orthe middle elastic member 23, or preferably both of them so thatrespective side portions become free ends. This is because at the timeof being seated or the like, respective side portions move upwards inthe drawing (in the direction of normal line) as if to roll in thedirection of rotation by the deformation accompanied by the input load,and a force in the shear direction is not generated so much, which helpsto disperse the input load. Accordingly, in order to display such afunction, the three-dimensional net member composing the middle elasticmember 23 is disposed with a tension higher than that of the upperelastic member 21, or in order to increase tolerance in deformation(degree of freedom) and to reduce a reaction force against a person, thethree-dimensional net member for the middle elastic member 23 isarranged so that the respective side portions become rotation-free ends.Further, a three-dimensional net member having the load bearingcharacteristic in the thickness direction is higher than that of theupper elastic member 21 or having a large deflection amount is adoptedso as to feel like a spring rich in elasticity.

[0057] Further, as the middle elastic member 23, any members can beadopted provided that it can prevent unnecessarily large depression ofthe upper elastic member 21 and has an elastic force capable ofdisplaying a predetermined feel of stiffness. Accordingly, it is notlimited to a three-dimensional net member. For instance, a felt formedin a predetermined thickness can be used as a third embodiment shown inFIG. 3, as a middle elastic member 33. It should be noted that thestructure of an upper elastic member 31 and the structure of a lowerelastic member 32 supported via a metal spring 35 in a cushion structure30 of the third embodiment shown in FIG. 3 are the same as those in thesecond embodiment.

[0058]FIG. 4 is a view showing a cushioning structure 40 relating to afourth embodiment of the present invention. The cushioning structure 40has a configuration specially suitable for using as a mat for bedding orthe like and is composed of an upper elastic member 41, a middle elasticmember 43, and a lower elastic member 42 piled vertically. Further, asexplained in the above-described embodiments, it is preferable todispose respective elastic members 41 to 43 without connectingrespective end portions thereof, but making them as free ends, therebyenabling input load to disperse so that the reaction force against aperson can be reduced. However, even in the case of connecting theserespective elastic member 41 to 43 by sewing or the like, if the endportions of respective elastic member 41 to 43 are connected in a stateto leave a room capable of creating similar deformation to that whenthey are made free ends, it becomes possible to bring a similar effectto the above-described effect due to the elasticity possessed byrespective elastic members. It is needless to say that an effect ofmaking a reaction force against a person small in quest of dispersing aninput load, by making ends of respective elastic members free ends, orby connecting respective elastic member leaving a deformable room (orspace), as described above, is not limited to the present embodiment butalso similar to other embodiments.

[0059] The upper elastic member 41, the middle elastic member 43, andthe lower elastic member 42 are all composed of a three-dimensional netmember, and in this embodiment, and are structured in layer withoutconnecting respective members to each other, which have different loadbearing characteristic from each other.

[0060] The upper elastic member 41 is, similarly to the upper elasticmember 11 of the first embodiment, the upper elastic member 21 of thesecond embodiment, and the upper elastic member 31 of the thirdembodiment, disposed to let the cushioning structure 40 provide afunction to set its load bearing characteristic to come close to theload bearing characteristic of muscle in a pressurizing process, and tomake the reaction force small in a small displacement area in arestoring process. Accordingly, the upper elastic member 41 is set tohave a soft load bearing characteristic with a low spring constant.However, in FIG. 4, there is no concave and convex portion, differentfrom those shown in FIG. 1 to FIG. 3. When a concave and convex portionis formed, since a convex portion is formed in a substantiallyarch-shaped cross section between adjacent concave portions, theconnecting yarn between ground knitted fabrics are disposed with aninclination, the convex portion serves to form an arch-shaped spring,and the elasticity in the bending direction and the horizontal directioncan be utilized. Accordingly, in a structure forming concave and convexportions, a soft spring constant that is close to the load bearingcharacteristic of a person, and has temporal set in fatiguecharacteristic under loads in which the reaction force is decreased in afixed deformation can be easily set up.

[0061] On the other hand, in the case of no concave and convex portionbeing formed, when compared with the case of forming concave and convexportions, the connecting yarn is disposed between confronting groundknitted fabrics without so much inclination, and the load bearingcharacteristic is determined mainly by buckling strength of theconnecting yarn. Therefore, when a soft load bearing characteristic likethe above-mentioned first to third embodiments is given without forminga concave and convex portion, a three-dimensional net member having afeeling of a soft spring can be obtained by designing the connectingyarn to be disposed at a predetermined inclination in advance at thetime of formation, or by selecting thickness and length of theconnecting yarn appropriately. It should be noted that when athree-dimensional net member is set to have a soft structure with afeeling of a spring by arranging the formation structure, it can beadjusted by either any one element or a combination of any two or moreelements among such an element as density of the connecting yarnarrangement, material of the connecting yarn, a stitch shape of theground knitted fabric, a stitch size of the ground knitted fabric,material of the ground yarn composing the ground knitted fabric, a knotfixing power at a joint portion between the connecting yarn and theground knitted fabric as well as the thickness and length of theabove-described connecting yarn. Needless to say, in the case of athree-dimensional net member forming concave and convex portions, byadjusting similar elements, it is possible to obtain a structure havinga feeling of various springs even the width of a concave and convexportion is similar to each other.

[0062] When a load area becomes more than a predetermined area, themiddle elastic member 43 is, similar to the middle elastic members 23and 33 relating to the above-described second and third embodiment,provided to prevent unnecessary depression of the upper elastic member41 disposed to display a soft load bearing characteristic in a smallload area, to increase a feeling of stability at the time of beingseated and lying by displacement created by the free ends and by afeeling of stiffness which the elastic member itself possesses, and atthe same time, to restrain a feeling of bottom touch of the upperelastic member 41 together with the lower elastic member 42. Forinstance, a three-dimensional net member formed to have a feeling of aspring harder than the upper elastic member 41.

[0063] The lower elastic member 42 is, similar to the lower elasticmember 12, 22 and 32 of the above-described first to third embodiments,disposed to prevent a feeling of bottom touch due to its elastic force,and a three-dimensional net member provided with a spring characteristichigh in linearity than that of the upper elastic member 41 is adopted.

[0064] It should be noted that as the middle elastic member 43 and thelower elastic member 42 in the fourth embodiment, it is not limited to athree-dimensional net member but it is possible to substitute them withother members having the above-described predetermined characteristicssuch as, for instance, felt, polyurethane foam, or the like.

[0065]FIG. 5 is a view showing a cushioning structure 50 relating to afifth embodiment. The cushioning structure 50 has a configurationsuitable for using as a mat for bedding or the like similar to thefourth embodiment, and six elastic members 51 to 56 consisting of athree-dimensional net members are structured in a vertical multilayer.

[0066] In the present embodiment, a first elastic member 51 disposed onthe top portion and a sixth elastic member 56 disposed on the lowermostportion are formed of a three-dimensional net member having concave andconvex portions, similarly to the upper elastic member 11 and the likeof the above-described first embodiment, and has a function to set itsload bearing characteristic to come close to the load bearingcharacteristic of muscle in a small area in the pressurizing process,and to make the reaction force small in a small displacement area in therestoring process, and a partial spring constant by a board for press of30 mm in diameter is set to be low so as to have a soft load bearingcharacteristic though a feel of stiffness in a wide area is high.

[0067] Among four layers of elastic members disposed between theabove-described first elastic member 51 and the sixth elastic member 56,a second elastic member 52 which is the second from the top in FIG. 5,and a fourth elastic member 54 which is the fourth from the top in FIG.5, are provided with a function corresponding to the middle elasticmember 23 in the above-described second embodiment and the like. When aload area becomes more than a predetermined area, the second elasticmember 52 and the fourth elastic member 54 are provided to preventunnecessary sink-in of the first and sixth elastic members 51 and 56provided to display a soft load bearing characteristic in a small loadarea, to increase a feeling of stability at the time of being seated andlying by its feeling of stiffness, and at the same time, to restrain areaction force to a person or a feeling of bottom touch by dispersion ofthe load.

[0068] On the other hand, a third elastic member 53 and a fifth elasticmember 55 are provided with a spring characteristic similar to thespring characteristic created by the lower elastic member 12 and themetal spring 15 of the above-described first embodiment, and the loadbearing characteristic by a board for press of 98 mm in diameter isclose to the load bearing characteristic of muscles of the haunches inthe area of 35 N to 100 N. It should be noted that the second to fifthelastic member 52, 53, 54 and 55 disposed between the first elasticmember 51 and the sixth elastic member 56 are acceptable so far as anyof them can mainly supply a feeling of stiffness and others can displaymainly a high feeling of spring, so that its order of layer or thenumber of layers are not limited. Further, in the present embodiment, inorder to enhance a load dispersion function, it is preferable to makethe end portions free similarly to the fourth embodiment.

[0069] Next, a structure of a three-dimensional net member 100 used asthe upper elastic member 11 in the first embodiment, the upper elasticmember 21 or the middle elastic member 23 in the second embodiment, theupper elastic member 31 in the third embodiment, the upper elasticmember 41, the middle elastic member 43 or the lower elastic member 42in the fourth embodiment, and the first to sixth elastic member 51 to 56in the fifth embodiment will be explained referring to FIG. 6 to FIG. 9.As shown in FIG. 6, the three-dimensional net member 100 is structuredof a solid three-dimensional structure including a pair of groundknitted fabrics 110 and 120 disposed apart from each other and a lot ofconnecting yarn 130 running between the pair of ground knitted fabrics110 and 120 to connect both.

[0070] One of the ground knitted fabrics 110 is formed with a flatknitted fabric structure (small mesh) structured with yarns made oftwisted monofilaments continuous to any directions in both waledirection and course direction as shown in FIG. 7, for instance. On theother hand, the other ground knitted fabric 120 is formed in a largerstitch structure than that of the ground knitted fabric 110 including ahoneycomb-like (hexagon) mesh made of twisted short filaments, as shownin FIG. 8 for instance. Needless to say, this knitted fabric structureis just an example, and it is possible to adopt knitted fabricstructures other than the small mesh structure or the honey combstructure. The connecting yarns 130 are knitted between the pair ofground knitted fabrics 110 and 120 to keep a predetermined distancebetween one of the ground knitted fabrics 110 and the other groundknitted fabric 120 so that a predetermined stiffness is given to thethree-dimensional net member 100 which is a solid mesh knitting.

[0071] The thickness or the like of the ground yarn forming the groundknitted fabrics 110 and 120 is not limited particularly, but selectedfrom that which can provide firmness in structure required for a solidknitted fabric and being in the range not to give difficulty in aformation work. As a ground yarn, a monofilament can be used, but it ispreferable to use a multifilament or a spun yarn from the point of viewsuch as feeling, softness in surface touch and so on.

[0072] It is preferable to use a monofilament as a connecting yarn 130,and it is suitable to use the one having a thickness in the range of 167to 1100 decitex. This is because a cushioning property having afavorable restoring force cannot be given by the multifilament, and whenthe thickness becomes lower than 167 decitex, it becomes difficult toobtain suitable firmness in structure. When it becomes more than 1100decitex, it becomes too hard to obtain a suitable spring property(cushioning property). In other words, adoption of the monofilamenthaving the above-described range as a connecting yarn 130 makes itpossible to support the load of a seated person by deformation of thestitch structure composing respective ground knitted fabrics 110 and120, and by falling down and buckling characteristic of the connectingyarn 130, and by restoring force of adjacent connecting yarn 130 givinga spring characteristic to the buckling characteristic, in other words,is possible to support by the buckling characteristic having a restoringforce, so that a soft structure having a soft spring characteristicwithout occurring of stress concentration can be realized. It should benoted that in the case of forming concave and convex portions, since aspring element having a cross section of substantially arch shape can beformed as will be described later, it is possible to give a furthersofter spring characteristic.

[0073] As a material for the ground yarn or the connection fiber 130, itis not limited to some special material and, for instance, syntheticfiber or regenerated fiber such as polypropylene, polyester, polyamide,polyacrylonitrile, rayon and so on, or natural fiber such as wool, silk,cotton and so on can be cited. The above material can be used alone orcan be used as any combination thereof. It is preferable to usethermoplastic polyester fibers such as polyethylene terephthalate (PET),and polybutylene terephthalate (PBT), polyamide fibers such as nylon 6and nylon 66, polyolefine fibers such as polyethylene and polypropylene,or a combination of two or more kinds of these fibers. Incidentally,polyester fibers is suitable because of its regeneration property. Itshould be noted that the shape of fibers used for the ground yarn or theconnecting yarn 130 is not limited, and a round cross sectional fiber, amodified cross sectional fiber and so on can be used.

[0074] As for the manner of arranging the connecting yarn 130 (pilestructure), when the connecting yarns 130 connecting respective groundknitted fabrics 110 and 120 are expressed from states seen from theside, more concretely, they are classified in the types shown in FIG. 9Ato FIG. 9E. FIG. 9A and FIG. 9B are a straight type in which theconnecting yarns 130 are knitted almost vertically between the groundknitted fabrics 110 and 120, and between the two, FIG. 9A is the oneknitted straight in the shape of the letter 8, and FIG. 9B is the oneknitted simply straight. FIG. 9C to FIG. 9E are cross types in which theconnecting yarns 130 are knitted to cross each other on the way betweenthe ground knitted fabrics 110 and 120. Among these, FIG. 9C is the oneknitted to cross the fibers in the shape of the letter of 8, FIG. 9D isthe one knitted in a cross simply, and FIG. 9E is the one knitted twofibers together in cross (double cross). It should be noted that, asshown in FIG. 9C to FIG. 9E, when the connecting yarn 130 are disposedslantwise in a cross with each other, it is possible to give a softspring characteristic having large compressibility while keeping asufficient restoring force due to buckling strength of respectiveconnecting yarn 130 compared with the pattern in which the connectingyarn 130 are disposed almost vertically between the ground knittedfabrics 110 and 120 (refer to FIG. 9A and FIG. 9B).

[0075] Here, when the above-described three-dimensional net member 100is used as the upper elastic members 11, 21, 31 of the above-describedfirst to third embodiments, and the first and sixth elastic members 51,56 of the fifth embodiment, it is processed into a structure havingconcave portions 150 and convex portions 160, as shown in FIG. 10 andFIG. 11. More concretely, the three-dimensional net member 100 isprocessed so that the pair of ground knitted fabrics 110 and 120 whichare disposed apart from each other at predetermined intervals along thecourse direction come close in the three-dimensional net member 100 toform concave portions 150, thereby forming convex portions 160 betweenadjacent concave portions 150 and 150.

[0076] Though the concave portion 150 can be formed from one side aloneout of the pair of ground knitted fabrics 110 and 120, it can be formedfrom both sides as shown in FIG. 10 and FIG. 11. As a means for formingthe concave portion 150 by allowing the ground knitted fabrics 110 and120 to come close to each other, a sewing means by sewing on a machine,or further such as interposing fusion fiber between the ground knittedfabrics 110 and 120 to bond them by melting the fusion fiber, as well asby welding, or by bonding. It is preferable to use a vibration weldingmeans among these means described above. It is because this means canprevent the welded portion to become stiff, and at the same time, thebonding strength is very high.

[0077] As above, by forming the concave portions 150, at the portionswhere the concave portions 150 are formed, the connecting yarns 130disposed in those area are tend to incline or bend, and further someconnecting yarns 130 move to the areas of adjacent convex portions 160via the concave portions 150 so as to be unevenly distributed.Accordingly, in these areas, nearby connecting yarns 130 are confoundedwith each other when being bonded. As a result of confoundly bonding asdescribed above, both sides of the connecting yarn 130 putting theconfounded portion 130 a inbetween can serve as respective independentspring elements (deforming elements) for the ground knitted fabric 110or the ground knitted fabric 120 which are respective bonding objects ofboth sides. Therefore, as schematically shown in FIG. 12, the area froma confounded portion 130 a where the connecting yarns 130 are confoundedin a concave portion 150 to another confounded portion 130 a where theconnecting yarns are confounded in a neighboring concave portion 150,formed is a structure taken to be serving as a spring element havingsubstantially an arch shaped cross section and a damping element due tofriction between yarns including the ground knitting fabric 110 and theconnecting yarns 130 disposed in this area.

[0078] As a result, in the three-dimensional net member having concaveand convex portions, the modulus of elasticity at the concave portion150 is different from that at the convex portion 160. When the convexportion 160 is compression-deformed due to an applied load, the bucklingstrength of the connecting yarn 130 becomes relatively small so that thebuckling characteristic becomes hard to exhibit compared with the caseof using the three-dimensional net member 100 without forming a concaveand convex portion, and as shown by an imaginary line in FIG. 12, anelastic function in the bending direction of the spring element having across section in a substantially arch shape including the confoundedconnecting yarn 130 becomes relatively large. In other words, in thespring characteristic of the convex portion 160 compared with athree-dimensional net member formed in the same condition except notforming a concave and convex portion, the spring constant is small andbecomes easy to start deforming from a very small load area, so that itsbuckling characteristic is hard to exhibit. As a result, athree-dimensional net member with a concave and convex portion becomessmall in a maximum value in the amount of hysteresis loss and becomeshigh in linearity compared with the case without a concave and convexportion. However, in its load bearing characteristic, an ordinarythree-dimensional net member shows a characteristic similar to aviscoelastic material of which restoring movement is delayed due to thehysteresis even the load becomes zero at the time of restoring, becauseof friction between the connecting yarns at the time of restoring of theconnecting yarn 13, and in a three-dimensional net member having aconcave and convex portion, the friction between yarns acts on theabove-described bending elasticity to cause further increase in thefriction between yarns at a concave portion. As a consequence, directionof the deformation and the like change according to an input, whichallows the spring element and the damping element corresponding to theinput to work.

[0079] Further, in the three-dimensional net member forming concave andconvex portions, elasticity expanding and contracting in substantiallyperpendicular to a formation line of the concave portion 150 is given byconfoundly bonding the connecting yarns 130 at the concave portion 150.Accordingly, when it is strained over seat frames or the like of a seatstructure, in addition to a spring property in the bending direction bya spring element having a substantially arch-shaped cross sectiongenerated in the thickness direction, elasticity (spring property)generated in the surface direction substantially perpendicular to thebending direction comes is added by the connecting yarn forming a springelement having a substantially arch-shaped cross section, and thiselongation further contributes to reduction of the spring constant.Furthermore, owing to the characteristic similar to a viscoelasticmaterial created by the increase of the friction between yarns, thedamping characteristic also gets large. Accordingly, by disposing theupper elastic member 11, the middle elastic members 23 and 33 aboverespective lower elastic members 12, 22, and 32 shown in theabove-described first to third embodiments at respectively predetermineddistances of intervals, elongation in lateral directions of respectiveupper elastic members 11, 21, and 31 composed of three-dimensional netmembers having concave and convex portions work effectively, delaycharacteristic of the restoring movement are revealed more remarkably,and the damping ratio also gets large.

[0080] Further, as shown in FIG. 13, when a portion protruded by a boneof the human body (corresponding nearly to a board for press having adiameter of 30 mm) comes in contact with a three-dimensional net member,the convex portions 160 on both sides of the concave portion 150sandwiched therebetween are depressively deformed as if running awaytoward outside and partial temporal set in fatigue under loads iscreated. Then, when the portion is further applied with a load andpressed in a large area, the whole three-dimensional net member comes tosupport the load, and since deformation as shown in FIG. 13 appears dueto the existence of such concave and convex portions, a feeling offitting is improved in a small displacement area.

[0081] The upper elastic members 11, 21, 31 and 41 of theabove-described respective embodiments and the first and sixth elasticmembers 51 and 56 of the fifth embodiment are provided with a softspring characteristic, and a reaction force in the range ofpredetermined amount of displacement or less is made small. However,when the amounts of the upper elastic members 11, 21, 31, 41 and so onare large, shear stress starts to serve on the muscles, which leads toincrease in a load on the muscles instead. Therefore, it is preferableto form respective upper elastic members 11, 21, 31, 41 and so on tohave a thickness including a pair of ground knitted fabrics (thethickness of the convex portion when concave and convex portions areformed) in the range of 5 to 30 mm, lest the maximum amount ofdeformation should be so large.

TEST EXAMPLE

[0082] The load characteristics of individual three-dimensional netmembers (test example 1 to 4) usable for the upper elastic member 11 ofthe first embodiment shown in FIG. 1, the upper elastic member 21 of thesecond embodiment shown in FIG. 2, the upper elastic member 31 of thethird embodiment shown in FIG. 3, the upper elastic member 41 of thefourth embodiment shown in FIG. 4, the first and sixth elastic members51 and 56 of the fifth embodiment shown in FIG. 5 are measured. Themeasurement is carried out by pressing a circular board for press of 200mm in diameter at a speed of 50 mm/minute. The results are shown in FIG.15.

[0083] The conditions of manufacturing the three-dimensional net membersused in test examples 1 to 4 are as follows. The three-dimensional netmember used in test example 1 has no concave and convex portion, and isstructured, as shown in FIG. 14, that space portions 210 are formedbetween ridge portions (band-shaped portion) 200 formed at intervals ofone wale or a plurality of wales. In the space portion 210, connectingportions 220 are formed over the range of 1 to several courses so as tobridge between the adjacent ridge portions 200. All of the test examples2 to 4 are formed with concave and convex portions as shown in FIG. 10and FIG. 11. A manufacturing condition for a comparison example is thesame as that for the test example 4 except that concave portions are notformed by vibration welding, and the compressibility is 13.2%, thecompression modulus of elasticity is 98.1%.

Test Example 1

[0084] knitting machine: Double Raschel knitting machine (9 guage/2.54cm, bed gap distance 15 mm)

[0085] wale density: 10 wale/2.54 cm

[0086] course density: 14 course/2.54 cm

[0087] finished thickness (distance between surfaces of a pair of groundknitted fabrics): 11.5 mm

[0088] ground yarn used in one ground knitted fabric: 1170 decitex/96fpolyester·BCF multifilament (crimped yarn)

[0089] ground yarn used in the other ground knitted fabric: 660decitex/192f polyester·BCF multifilament (crimped yarn)

[0090] connecting yarn: 660 decitex/1f polyester

[0091] structure of one ground knitted fabric: derivative stitch of 2course mesh

[0092] structure of the other ground knitted fabric: queen's cord

[0093] total thickness of a stitch formed with ground yarn in one groundknitted fabric and connecting yarn: 1830 decitex, (partially 3000decitex)

[0094] total thickness of a stitch formed with ground yarn in the otherground knitted fabric and connecting yarn: 1980 decitex

[0095] compressibility of ridge portion: 49.5%

[0096] compression modulus of elasticity of ridge portion: 98.8%

[0097] difference in compressibility between ridge portion and otherportions: 5.2%

[0098] width of ridge portion: 6 wales

[0099] width of space portion: 1 wale

Test Example 2

[0100] knitting machine: Double Raschel knitting machine (9 guage/2.54cm, bed gap distance 15 mm)

[0101] wale density: 10 wale/2.54 cm

[0102] course density: 14 course/2.54 cm

[0103] finished thickness (distance between surfaces of a pair of groundknitted fabrics): 11.5 mm

[0104] ground yarn used in one ground knitted fabric: 1170 decitex/96fpolyester→BCF multifilament (crimped yarn)

[0105] ground yarn used in the other ground knitted fabric: 660decitex/192f polyester→BCF multifilament (crimped yarn)

[0106] connecting yarn: 660 decitex/1f polyester

[0107] structure of one ground knitted fabric: derivative stitch of 2course mesh

[0108] structure of the other ground knitted fabric: queen's cord

[0109] total thickness of a stitch formed with ground yarn in one groundknitted fabric and connecting yarn: 1830 decitex, (partially 3000decitex)

[0110] total thickness of a stitch formed with ground yarn in the otherground knitted fabric and connecting yarn: 1980 decitex

[0111] compressibility of convex portion: 57.9%

[0112] compression modulus of elasticity of convex portion: 98.8%

[0113] difference in compressibility between convex portion and concaveportion: 57.8%

[0114] vibration welding condition of concave portion: applied pressure18.2 kgf/m², amplitude 1.0 mm, time period 1.2 sec

[0115] width of convex portion: 5 wales

[0116] width of concave portion: 2 wales

Test Example 3

[0117] knitting machine: Double Raschel knitting machine (9 guage/2.54cm,

[0118] bed gap distance 15 mm)

[0119] wale density: 9.8 wale/2.54 cm

[0120] course density: 12.8 course/2.54 cm

[0121] finished thickness (distance between surfaces of a pair of groundknitted fabrics): 12.05 mm

[0122] ground yarn used in one ground knitted fabric: 1170 decitex/384f

[0123] ground yarn used in the other ground knitted fabric: 560decitex/70f

[0124] connecting yarn: 560 decitex/1f

[0125] structure of one ground knitted fabric: 1 repeat 2 course mesh

[0126] structure of the other ground knitted fabric: queen's cord

[0127] total thickness of a stitch formed with ground yarn in one groundknitted fabric and connecting yarn: 1730 decitex

[0128] total thickness of a stitch formed with ground yarn in the otherground knitted fabric and connecting yarn: 1120 decitex

[0129] compressibility of convex portion 89.1%

[0130] compression modulus of elasticity of convex portion: 100%

[0131] difference in compressibility between convex portion and concaveportion: 89.0%

[0132] vibration welding condition of concave portion: applied pressure21.7 kgf/m², amplitude 1.0 mm, time period 1.0 sec

[0133] width of convex portion: 6 wales

[0134] width of concave portion: 2 wales

Test Example 4

[0135] knitting machine: Double Raschel knitting machine (9 guage/2.54cm, bed gap distance 15 mm)

[0136] wale density: 9 wale/2.54 cm

[0137] course density: 13.5 course/2.54 cm

[0138] finished thickness (distance between surfaces of a pair of groundknitted fabrics): 11.5 mm

[0139] ground yarn used in one ground knitted fabric: 1170 decitex/96f

[0140] ground yarn used in the other ground knitted fabric: 660decitex/192f

[0141] connecting yarn: 660 decitex/1f

[0142] structure of one ground knitted fabric: convex portion→1 repeat 4course mesh, concave portion→modified W atlas

[0143] structure of the other ground knitted fabric: queen's cord

[0144] total thickness of a stitch formed with ground yarn in one groundknitted fabric and connecting yarn: 2050 decitex (partially 3220decitex)

[0145] total thickness of a stitch formed with ground yarn in the otherground knitted fabric and connecting yarn: 1540 decitex

[0146] compressibility of convex portion: 20.0%

[0147] compression modulus of elasticity of convex portion: 94.3%

[0148] difference in compressibility between convex portion and concaveportion 310: 6.8%

[0149] vibration welding condition of concave portion: applied pressure18.2 kgf/m², amplitude 1.0 mm, time period 1.2 sec

[0150] width of convex portion: 9 wales

[0151] width of concave portion: 3 wales

[0152] Incidentally, the compressibility and the compression modulus ofelasticity are measured according to a test method based on JASOStandard M404-84 “Compressibility and Compression modulus ofelasticity”. More concretely, three sheets of samples in the size of 50mm×50 mm are prepared, and respective thickness are measured after aninitial pressure of 3.5 g/cm² (0.343 kPa) is applied on each of thesamples in the thickness direction for 30 seconds. Then, the thicknessof the samples are measured at the time of keeping them for 10 minutesunder the pressure of 200 g/cm² (19.6 kPa). Then, after keeping thesamples for 10 minutes with the loads being removed, a pressure of 3.5g/cm² (0.343 kPa) is applied again for 30 seconds and the thickness ismeasured. The compressibility and the compression modulus of elasticityare calculated based on the following equations and expressed in anaverage value of three samples respectively.

Compressibility (%)={(t ₀ −t ₁)/t₀}×100  Equation 1

Compression modulus of elasticity (%)={(t ₀ −t ₁)/(t ₀ t₁)}×100  Equation 2

[0153] Here, to indicates a thickness (mm) of the sample when a pressureof 3.5 g/cm² (0.343 kPa) is applied, t₁ indicates a thickness (mm) ofthe sample when a pressure of 200 g/cm² (19.6 kPa) and t′₀ indicates athickness (mm) of the sample when a pressure of 3.5 g/cm² (0.343 kPa) isapplied again.

[0154] As is clear from FIG. 15, when the load bearing characteristic inthe go-process (pressurizing process) till the upper initial load rangeof 200 N (about 20 kg) while using a board for press of 200 mm indiameter is observed, it is found that the spring constant in each testexample is lower than that in the comparison example having lowcompressibility and high compression modulus of elasticity. Further,when the test example 1 which forms no concave and convex portion andthe test example 2 which forms concave and convex portions are compared,the test example 2 which forms concave and convex portions shows a lowerspring constant and a softer load bearing characteristic. This isbecause by utilizing mainly the spring property in a bending directionowing to a spring element having a substantially arch-shaped crosssection, the hysteresis loss becomes small and the linearity becomeshigh compared with an ordinary three-dimensional net member having ahigh friction coefficient owing to its buckling characteristic and knotfixing strength.

[0155] In the return process (restoring process), though both are foundto have spring constants lower than those in the pressurizing processdue to the hysteresis loss, in the case of the comparison example, thespring constant in the restoring process even in the displacement rangeof 2 to 1 mm is still about 40 N/mm, and the reaction force remains tillthe displacement amount becomes nearly 0 mm. On the other hand, in thecase of test examples 1 to 4, after the displacement amount comes to 1mm at the latest in the restoring process, the structure is found tohave a very small reaction force such that the spring constant becomesmuch lower than the spring constant in the pressurizing process of allthe cushioning structure in each embodiment which will be describedlater, and becomes nearly zero. This load bearing characteristic ismeasured by pressing with a board for press of 200 mm in diameter at aspeed of 50 mm/min. In the load bearing characteristic of athree-dimensional net member alone, it is required as described above tohave a function to improve a feeling of fitting in a small displacementarea by a partial displacement. Therefore, a characteristic of a springcharacteristic to become nearly zero after the displacement amount of 20mm or less comes to 1 mm in the above-described restoring process canpreferably exhibit at the time of being pressed with a board for pressof 30 mm in diameter at a speed of 50 mm/min (refer to FIG. 13).

[0156] (Embodiments 1 to 5)

[0157] Load bearing characteristics are measured for the wholecushioning structures relating to the first embodiment shown in FIG. 1(embodiment 1), the second embodiment shown in FIG. 2 (embodiment 2),the third embodiment shown in FIG. 3 (embodiment 3), the fourthembodiment shown in FIG. 4 (embodiment 4), and the fifth embodimentshown in FIG. 5 (embodiment 5). It should be noted that thethree-dimensional net member used for the upper elastic members 11, 21,and 31 in the embodiment 1 to 3, and the first and sixth elastic members51 and 56 in the embodiment 5 is used in the above-described testexample 2 which is strained at the elongation percentage of zero and thelongitudinal direction of the convex portion is along the direction ofgap between the side frames. In the embodiment 4, the elastic memberadopted in the above-described test example 1 is used as the upperelastic member 41. The measurement is carried out by pressing a circularboard for press of 98 mm in diameter from a surface of thethree-dimensional net member to 100 N at a speed of 50 mm/minute. Theresult is shown in FIG. 16. Further, for the muscles of haunches of aperson, the load bearing characteristic is measured similarly bypressing with a circular board for press of 98 mm in diameter and theresult is shown in the same figure.

[0158] In all of respective lower elastic members 12, 22, and 32 inembodiments 1 to 3, the same Plumaflex is strained by 4 pieces of metalsprings on the right and left respectively. The adopted metal spring isa coil spring having 2.6 mm in wire diameter, 54.6 mm in coil length,16.1 mm in coil average diameter, 20 in winding number, and 0.55 N/mm inspring constant.

[0159] As is clear from FIG. 16, spring constants of the load bearingcharacteristic in the go-process (pressurizing process) are all in therange of 0.1 to 10 N/mm, and at the same time, the amounts of hysteresisloss are in the range of 10 to 20 N, and especially in the area of 35 to100 N which is over the load equilibrium point, it shows a low springconstant close to the spring characteristic of muscles. Incidentally, apreferable spring constant is in the range of 0.1 to 5 N which is closerto the spring constant of muscles. The amount of hysteresis loss ispreferably in the range of 10 to 20 N as a characteristic whenmeasurement is carried out by pressing with a board for press of 98 mmin diameter as described above, but the range below 40 N is acceptable.

[0160] On the other hand, in a return process (restoring process) of theload bearing characteristic, embodiment 1, embodiment 2, and embodiment4 show the spring constants after the displacement amounts come to about3 to 5 mm which is before the displacement amount comes to zero or thetested samples are completely restored, becomes substantially zero whichis lower than the spring constant of muscles. Further in embodiment 3and embodiment 5, when the displacement amounts come to about 15 to 18mm before it becomes zero or the tested samples are completely restored,the spring constant thereafter becomes substantially zero. In otherwords, in the load bearing characteristic of the three-dimensional netmember alone in the above-described test example 2, the spring constantcomes to near zero at the time of the displacement amount to be about 2mm. However, by making it into a layered cushioning structure as in theembodiments, it is found that the range to get near zero of the springconstant is widened.

[0161] From the above, by disposing to a three-dimensional net memberanother elastic member to prevent bottom touch in layers, and ifnecessary, by arranging still another elastic member such as a metalspring, Plumaflex, or the like which is high in surface stiffness,capable of preventing a feeling of something foreign in layers, it isfound that a spring constant which does not allow a seated person tofeel a reaction force can be provided in an area below the predetermineddisplacement amount, more concretely, in an area from the displacementamount of 20 mm to 2 mm at the latest considering the data in theabove-described embodiments, for instance, after the displacement amountcomes to about 15 mm or less in embodiment 3. Through this arrangement,in the range of displacement from several millimeters to ten and severalmillimeters or so, the structure tends to bend under a small load due tothe spring constant of 0.1 to 10 N/mm or less, which is close to musclesduring pressurizing process, but since it causes only temporal set infatigue due to the load with almost no inputting of the reaction forcethereof, the cushioning structures in respective embodiments only givethe seated person a feeling of light touch on a small contact area as inthe case of coming in contact with a portion protruded by a bone of thehuman body, and there is no reaction force which causes a blood streamtrouble or loads on muscles. Therefore, a feeling of seating with afeeling of being safe can be obtained.

[0162] (Embodiment 6)

[0163] A three-dimensional net member (embodiment 6) with concave andconvex portions as shown in FIG. 10 and FIG. 11 is mounted on a planeboard, and the load bearing characteristic is measured while changingthe size (diameter) of a board for press. The results are shown in FIG.17 to FIG. 19. FIG. 17 shows the case of pressurizing to 100 N with aboard for press of 30 mm in diameter, FIG. 18 shows the case ofpressurizing to 100 N with a board for press of 98 mm in diameter, andFIG. 19 shows the case of pressurizing to 1000 N with a board for pressof 200 mm in diameter. It should be noted that all of the speed of theboard for press are 50 mm/minute. Further, in all cases, similarmeasurement is carried out for a three-dimensional net member (forcomparison) with no concave and convex portion prepared under completelythe same condition as in embodiment 6 except no formation of concave andconvex portion by vibration welding.

[0164] As is clear from FIG. 17, when pressurized with a board for pressof 30 mm in diameter, embodiment 6 is found to be low as a whole in aload value against a displacement amount compared with the comparisonexample, and a displacement amount in which the spring constant duringthe restoring process comes to zero is found to be increased.Accordingly, it is found that it tends to displace partially, and when aprotruded portion comes in contact, the reaction force at that time issmall. As shown in FIG. 18, when pressurized with a board of 98 mm indiameter (corresponding to the one side size of human haunches), a loadvalue against a displacement amount is lowered as a whole similarly,compared with the comparison example. The spring constants both in thepressurizing process and the restoring process are lowered and whencompared with the comparison example, the reaction force is found to besmall. However, the linearity gets higher compared with the case ofpressurizing with the board of 30 mm in diameter in FIG. 17, which showsthat the surface stiffness becomes high by increment of pressurizedarea. In the case of pressurizing with the board for press of 200 mm indiameter in FIG. 19, the linearity is similarly enhanced and the surfacestiffness is increased compared with the case of the comparison example.

[0165] As above, it can be said that it becomes clear from theexperiment result that by making a structure including concave andconvex portions as in embodiment 6, in the case of a small contact area,the structure gives only a seated person a feeling of light contact, andcreates no reaction force which may cause a blood stream trouble orloads on muscles, and in the case of a large contact area, the structurecan exhibit a sufficient surface stiffness, absorbs physique differencesbetween seated persons to give a feeling of seating with a feeling ofbeing safe.

[0166] Here, in a case that a cushioning structure according to thepresent invention is applied to a sitting seat, it is preferable that ata portion coming into contact with haunches, namely at a seat cushionportion, when a portion protruded by a bone is abutted, it can createtemporal set in fatigue under loads while being partially bent as shownin FIG. 20, and as shown in FIG. 21, when a load is further applied, ithas a structure that can support the load with a wider area according tothe size of the inputted figure (shape and size of the haunches). Thisis because that since there is little difference of physique in shapeand size of the haunches, when a load more than predetermined isapplied, it enhances its vibration absorbability by serving the springproperty sufficiently. Therefore, in a seat cushion portion, similarlyto each embodiment described above, it is preferable to use such astructure that on an elastic member having a small reaction force suchas a three-dimensional net member with concave and convex portions,another elastic member (such as Plumaflex, a metal spring, or the like)having a spring property is disposed, or if necessary, still anotherelastic member having a high surface stiffness is disposed.

[0167] On the other hand, in a seat back portion, a difference inphysique is exhibited more clearly than the haunches due to a skeletalstructure, and a difference in a position protruded by bones is largercompared with the haunches. Accordingly, it is preferable for acushioning structure to form a seat back portion to put emphasis on afunction to absorb a difference in physique. From this point of view,the conventional cushioning structure of using a polyurethane foam isinsufficient in respect of a physique difference absorbing function,because, as shown in a imaginary line in FIG. 22B, the whole cushion isbent backwards around a substantially central portion of the seat backpotion so that both sides are drawn nearly to the central portion. Onthe contrary, when the three-dimensional net members explained in theabove-described respective embodiments are used and strained at anelongation percentage of less than 5%, a structure can be obtained inwhich, as shown in FIG. 23, it can create a partial temporal set infatigue under loads in a small load range and displacement area, and, asshown in FIG. 22A, even when a further load is applied on it, it canfollow the skeletal structure to absorb the difference in physique, anddeform while fitting to the body by a damping characteristic due tofriction between yarns. Therefore, in a cushioning structure composing aseat back portion, it is recommendable to make a structure to use, forinstance, a three-dimensional net member with concave and convexportions explained in the above-described respective embodiment as anelastic member and only strain it, but not to dispose other elasticmembers.

[0168] Through this formation, in a seat cushion portion, as shown inFIG. 24A and FIG. 24B, a cushioning structure putting emphasis mainly ona spring element can be formed, and in a seat back portion, a cushioningstructure putting emphasis mainly on a damping element can be formed.Therefore, the present invention has a merit of realizing a sitting seatstructure provided with such ideal functions by selecting a combinationof cushioning structures easily and at low costs.

[0169] According to FIGS. 24A and 24B, for a seat cushion portion, acushioning structure of the present invention in which Plumaflex issupported with right and left total 8 pieces of metal springs (coilspring) and a three-dimensional net member with concave and convexportions is arranged thereon is adopted (refer to FIG. 1), and for aseat back portion, only a three-dimensional net member with concave andconvex portions is adopted as a cushioning structure of the presentinvention, to prepare a car seat and respective load bearingcharacteristics are measured. It should be noted that thethree-dimensional net members are supported at an elongation percentageof zero.

[0170]FIG. 25 shows load bearing characteristics of the cushioningstructure adopted for the seat cushion portion, in which a broken lineshows a load bearing characteristic combined both of the metal springsand Plumaflex, a thin solid line shows a load bearing characteristic ofthe whole cushioning structure layered with three-dimensional netmembers, and a bold solid line shows a spring constant (k) of the wholecushioning structure. As is clear from the drawing, it is found thatlinearity is high and the spring characteristic contributes to a highdegree because the metal springs and Plumaflex are arranged to thethree-dimensional net member in layers. Incidentally, after about 8 toabout 10 mm in the restoring process, the spring constant comes tonearly zero, and temporal set in fatigue under loads is generated in asmall displacement area.

[0171]FIG. 26 shows a load bearing characteristic of the cushioningstructure adopted for the seat back portion, namely the cushioningstructure consisting of only a three-dimensional net member with concaveand convex portions. Incidentally, a bold solid line shows a loadbearing characteristic of the haunches. From this result, it is foundthat in the cushioning structure adopted for the seat back portion,hysteresis loss becomes large compared with that in the seat cushionportion, showing large contribution of the damping element. Further, itis also found that the load bearing characteristic of this cushioningstructure is almost parallel to the load bearing characteristic of thehaunches, and has a characteristic close to the load bearingcharacteristic of the muscle. Incidentally, after the displacementamount of about 20 mm in the restoring process, the spring constant isnearly zero.

[0172] Then, a person of JM96 (cushion share load: 85 kg) is seated onthe above-described seats, a vibrator platform is disposed below theseat cushion portion, and acceleration transmittance against frequency(G/G) is measured. The result is shown by a broken line in FIG. 27. Forcomparison, a vibration characteristic of a seat using polyurethane foamis shown by a thin solid line, and a vibration characteristic of a seatusing an ordinary three-dimensional net member without concave andconvex portion (provided that other conditions except no concave andconvex portion are the same as that for the seat of the presentinvention) is shown by a bold solid line.

[0173] Although if the acceleration transmittance (G/G) exceeds 2.0, itgives a bad effect to a feeling of riding comfort, but as for this pointthey are all restrained to a low vibration transmittance. However,compared with a seat using polyurethane foam, all of the seat using athree-dimensional net member has a slightly lower vibrationtransmittance, and shows a favorable characteristic.

[0174] It has been known that a factor affecting a riding comfortlargely is vibration of 2 Hz or less and 5 Hz which shakes a skeletalstructure itself by vibration. Accordingly, it is desirable that theresonance peak should keep away from these ranges and the accelerationtransmittance of 6 to 8 Hz which makes resonance with the internalorgans should be lowered. As for this point of view, when the cushioningstructure of the present invention is used, the resonance peak is setbetween 2 Hz and 5 Hz, and the frequency is set to be lower than thoseof other two cushioning structures. Accordingly, the accelerationtransmittance in the range of 6 Hz to 8 Hz at which the internal organresonates is set to be remarkably lower than those of other twocushioning structures. Therefore, it is found that when the cushioningstructure of the present invention is used, it is also very excellent ina point of vibration absorbency.

INDUSTRIAL AVAILABILITY

[0175] The cushioning structure of the present invention includes anelastic member composed of a three-dimensional net member formed byconnecting a pair of ground knitted fabrics disposed apart from eachother using connecting yarn, and a spring constant during a pressurizingprocess is set in the range of 0.1 to 10 N/mm and, at the same time,during a restoring process, a spring constant after restoring to anamount of displacement of 20 mm or less, at the latest, to 2 mm, is setto be lower than the spring constant during the aforementionedpressurizing process. As a result, when a person comes into contact witha cushioning member by a sitting movement or a standing movement,temporal set in fatigue under loads (stroke) of about severalmillimeters to about ten and several millimeters is created, therebyimproving a feeling of fitting (compatibility) which makes a person feelcomfortable, and effectively alleviate a blood stream trouble and loadson muscles. Therefore, when the cushioning structure of the presentinvention is applied especially to a seat structure of aircraft, it iseffective to prevent a trouble so-called an economy-class syndrome whichis caused by blood stream trouble or loads on muscles.

1. A cushioning structure including an elastic member composed of athree-dimensional net member formed by connecting a pair of groundknitted fabrics disposed apart from each other using connecting yarn,wherein, as a load bearing characteristic of the cushioning structure, aspring constant during a pressurizing process is set in the range of 0.1to 10 N/mm and, at the same time, during a restoring process, a springconstant after restoring to an amount of displacement of 20 mm or less,at the latest, to 2 mm, is set to be lower than the spring constant inthe aforementioned pressurizing process.
 2. The cushioning structureaccording to claim 1, wherein the spring constant in the aforementionedpressurizing process is set in the range of 0.1 to 5 N/mm.
 3. Thecushioning structure according to claims 1 or 2, wherein the amount ofhysteresis loss between the pressurizing process and the restoringprocess in the load bearing characteristic is in the range of 40 N orless.
 4. The cushioning structure according to any one of claim 1 toclaim 3, wherein the elastic member composed of the three-dimensionalnet member is configured to have a small reaction force such that as aload bearing characteristic during the pressurizing process thethree-dimensional net member with a board for press of 30 mm in diameteralone, a spring constant after restoring to an amount of displacement of20 mm or less, at the latest, to 1 mm during the restoring process islower than the spring constant during the pressurizing process in thewhole load bearing characteristic.
 5. The cushioning structure accordingto claim 4, wherein said three-dimensional net member formed in astructure having a small reaction force has a thickness in the range of5 to 30 mm.
 6. The cushioning structure according to claim 4 or claim 5,wherein said three-dimensional net member formed in a structure having asmall reaction force is provided with concave and convex portions atleast on one surface, and the elasticity of the concave portion and thatof the convex portion are different from each other. 7 The cushioningstructure according to claim 6, wherein said three-dimensional netmember formed in a structure having a small reaction force has astructure in which the convex portion is formed substantially in an archshaped cross section between adjacent concave portions, and theelasticity in a bending direction of the convex portion having thesubstantially arch shaped cross section and the damping caused byfriction accompanying sliding of the connecting yarn disposed in theconcave portions can be utilized.
 8. The cushioning structure accordingto any one of claims 4 to 7, wherein another elastic member serving as afunction to prevent the cushion from bottom touch during thepressurizing process is provided below an elastic member composed ofsaid three-dimensional net member formed in a structure with a smallreaction force. 9 The cushioning structure according to claim 8, whereinaforementioned another elastic member serving as a function to preventthe cushion from bottom touch is a net type elastic member, a sheet typeelastic member, or a net or sheet type elastic member supported viametal springs.
 10. The cushioning structure according to claim 8 orclaim 9, wherein aforementioned another elastic member serving as afunction to prevent bottom touch is disposed at a predetermined intervalto the elastic member composed of a three-dimensional net member formedin a structure with a small reaction force.
 11. The cushioning structureaccording to any one of claim 4 to claim 9, wherein still anotherelastic member higher in surface stiffness than the elastic membercomposed of the three-dimensional net member formed in a structure witha small reaction force is layered, in addition to the elastic membercomposed of said three-dimensional net member formed in a structure witha small reaction force and aforementioned another elastic member servingto prevent bottom touch.
 12. The cushioning structure according to claim11, wherein an elastic member composed of the three-dimensional netmember formed in a structure with a small reaction force is laminated onthe upper portion of still another elastic member described above, andanother elastic member described above serving as a function to preventbottom touch is arranged on the lower portion of still another elasticmember described above at a predetermined interval.
 13. The cushioningstructure according to any one of claim 1 to claim 12, wherein thecushioning structure is applied to various seat structures including avehicle seat and a furniture chair or a mat for furniture or forseating.
 14. The cushioning structure according to claim 13, wherein thecushioning structure is applied to a seat structure for an aircraft.